Tag Archives: lunar cycle

This star map shows the Houston sky at 9 p.m. CST on Feb. 1, 8 p.m. CST on Feb. 14, and 7 p.m. on Feb. 28. To use the map, put the direction you are facing at the bottom. The Great Square of Pegasus sets in the western sky. Taurus, the Bull, is almost overhead. Dazzling Orion, the Hunter is high in the south, with his two dogs behind him. Sirius, the Big Dog Star, is the brightest star we ever see at night. Jupiter, in Gemini, approaches the zenith on February evenings. Look for Canopus, the second brightest star ever seen at night, low in the south.

This month, Venus has entered the morning sky. Look southeast at dawn for the brightest point of light there; only the Sun and Moon outshine Venus. Venus remains a morning star for almost all of 2014.

Jupiter, up literally all night long last month, remains well placed for evening observing all winter and spring. Look for it in the east at dusk and almost overhead later in the evening.

Mars remains in the morning sky. It continues to brighten a bit in the south at dawn.

Saturn remains in the pre-dawn sky. Face south-southeast right before sunup to see it.

In February, the Big Dipper only partly risen at dusk. Its two pointer stars — the stars farthest from the handle which point at the North Star —may be high enough to see over trees and buildings.

Watch the Great Square of Pegasus set in the west at dusk. Taurus the Bull is high in the south. Look for the Pleiades star cluster above reddish Aldebaran. Dazzling Orion the Hunter takes center stage on winter evenings. Surrounding Orion are the brilliant stars of winter. Orion’s belt points down to Sirius, the Dog Star, which outshines all other stars we ever see at night. The Little Dog Star, Procyon, rises with Sirius and is level with Orion’s shoulder as they swing towards the south. To the upper left of Orion’s shoulder is Gemini, the Twins, which contains Jupiter this winter.

Under Sirius and low to the southern horizon this month is a star that most Americans never get to see: Canopus. Representing the bottom (keel) of the legendary ship Argo, Canopus is the second brightest star ever visible at night (second to Sirius). Thus, it is clearly noticeable along the southern horizon on February and March evenings. However, you must be south of 37 degrees north for Canopus to rise. (This is the line that divides Utah, Colorado, and Kansas from Arizona, New Mexico, and Oklahoma.)

The sky we see depends on our latitude as well as on the time of night and time of year. From any given location in our hemisphere, there is an area of the sky around the North Star in which stars never set (circumpolar stars), and an equivalent area around the South Celestial Pole in which stars never rise. The closer you are to the pole, the larger these areas are. Observers in Canada, for example, have many circumpolar stars, but there is also a large area of stars that they never see. The closer you get to the equator, the fewer circumpolar stars there are, but there are also fewer stars that never rise for you. At the equator, no stars are either circumpolar or never visible; all of them rise and set as Earth turns.

That’s why, down here in south Texas, the Big Dipper sets, although it’s always up for most Americans. On the other hand, Canopus, too far south to rise for most Americans, rises here.

The Moon takes 27.34 days to orbit Earth; one cycle of Moon phases lasts 29.54 days. At 28 days long, February is the only month shorter than a lunar phase cycle, and thus the only month that can have only three of the four main phases. That’s the case this year, as a New Moon occurred at the end of January and the next comes early on March 1.

On most clear Saturday nights at the George Observatory, you can hear me do live star tours on the observation deck with a green laser pointer. If you’re there, listen for my announcement.

Like most Americans, I learned the sky as imagined by westerners around the Mediterranean basin, with images from Babylon, ancient Egypt, ancient Greece and Rome, and star names preserved during the Middle Ages by Arabs. So I find it fascinating to think of an entirely different culture and how they imagined the night sky. The Chinese New Year celebration is a perfectly appropriate time to do this, especially since objects in the sky, in particular the moon and Jupiter, serve as the basis of the ancient Chinese calendar.

The date of Chinese New Year varies; it can occur as early as Jan. 21 or as late as Feb. 19. However, anyone familiar with the lunar cycle can easily predict the date for a given year. That’s because China’s New Year always begins with the second new moon after the winter solstice.

Our Gregorian calendar is a solar calendar, based on the apparent position of the sun (and thus, on the Earth’s orbit around the sun). However, the apparent position of the sun compared to the stars is difficult to observe. Much more readily observable are the phases of the moon. Thus the Chinese, like many ancient cultures, adopted a lunar calendar, measuring months from new moon to new moon. Unlike the Islamic or ancient Roman calendars, the Chinese calendar begins months with the dark of the moon–the day the moon is invisible, not the first slender crescent seen at dusk.

It would be convenient if one year equaled an even number of phase cycles. In fact, however, the moon takes about 29.5 days to go through one phase cycle, so 12 such cycles is 354 days. This is significantly less than the solar year of 365.25 days, so a purely lunar calendar quickly becomes disconnected from the seasons and useless as a guide for when to plant or harvest. To keep their lunar months connected with the seasons, the Chinese added a rule: the second-to-last lunar month must contain the winter solstice. If the old crescent moon of the eleventh lunar month is waning towards new and the winter solstice has not yet happened, that month is repeated. Similar rules exist for the second lunar month (which must contain the spring equinox), the fifth lunar month (which must contain the summer solstice), and the eighth lunar month (which must contain the fall equinox). Accordingly, the first new moon after the winter solstice always begins the last month in the Chinese year, and the second new moon after the solstice begins the next year.

Chinese astronomers noticed that every twelve years, Jupiter reappears next to the same stars. (This is because Jupiter takes 11.86 years to orbit the Sun.) There were twelve months in a typical Chinese year (although occasionally one was doubled, as explained above). Also, the Chinese divided the day into twelve double-hours. They used a system of twelve ‘Earthly Branches’ to designate the months of the year and the double-hours in a day. Jupiter’s motion in the sky established a cycle of years analogous to the cycles of months and double-hours. Thus Jupiter became the ‘Year Star’ (Suixing) and years, too, were designated with the Earthly Branches.

Later, as a mnemonic device, the Chinese began to associate the Earthly branches with animals. (Sources disagree as to exactly when.) Legends tell that Buddha (or the Jade Emperor) summoned all of the animals to him; each of the first twelve to appear became associated with an Earthly Branch. The twelve animals are:

The signs of the Chinese zodiac, then, unlike those of the western zodiac, are not constellations in the sky. The most well known of the Chinese constellations are the 28 ‘lunar mansions.’ These are small groups of stars very roughly arrayed along the ecliptic, which is the apparent path of the sun, moon and planets across the sky. As you’ll see in the links below, the Chinese used some stars, such as those in Orion, that are too far from the ecliptic for the moon to pass through them. The 28 mansions were subdivided into four groups of seven; each group of seven represented one of four Chinese animals associated with the directions and the seasons:

1) The Blue/Green Dragon (Qing Long) of the East, associated with spring. Note that the ancient Chinese color word qing was quite broad in meaning. Blue and green were considered different shades of this broadly defined color.

2) The Red Bird (Zhu Que) of the South, associated with summer. This mythical bird, with red and orange plumage, is distinct from the feng huang, also called the Chinese phoenix.

4) The Black Tortoise (literally Dark Warrior, Xuan Wu) of the North, associated with winter. Xuan Wu was always shown as a tortoise with a snake wrapped around it, reflecting the folkloric belief that all tortoises were female and needed to copulate with snakes to reproduce.

Of the stars in tonight’s evening sky, those in Orion and Taurus form part of the White Tiger, while Gemini and the dimmer stars south and east of it belong to the Red Bird.

Along with the four large animals, Chinese astronomers defined three large constellations known as the three enclosures. The largest of these is the ‘Purple Forbidden Enclosure‘ (Zi Wei Yuan) which includes all those stars near the North Pole of the sky which never set as seen from mid-northern latitudes. The enclosure is ‘forbidden’ because it includes the North Star, which was the Emperor of Heaven because it always remains in one spot while other stars seem to go in circles around it, as if paying court.

The ‘Supreme Palace Enclosure‘ (Tai Wei Yuan) actually rises in the late evening in February. Look east about 9 tonight for a set of stars in the shape of a backwards question mark. We see this as the head of Leo, the Lion. Rising under the backwards question mark is a right triangle of similar brightness. For us, this is Leo’s hindquarters, but in China, it’s the northwest corner of the Supreme Palace enclosure. The other side of this enclosure is a semi-circle of stars westerners recognize as part of Virgo, the Virgin.

The final enclosure, the ‘Heavenly Market Enclosure‘ (Tian Shi Yuan), won’t rise until very early in the morning in February, and isn’t in the evening sky until late May. It centers on our constellations Ophiuchus and Serpens (Caput and Cauda), just north of the bright summer constellations Scorpius and Sagittarius.

So, I wish everyone a happy Year of the Tiger. I’ll celebrate it by looking at the stars in a way I ‘m not accustomed to seeing them.